Navigation device, navigation method, and navigation program

ABSTRACT

A navigation device for a route guidance includes: a GPS unit that acquires information about the current location by performing a communication with a global positioning system (GPS); a navigation-information acquiring unit that acquires map data and route data from a navigation server in a network; a guidance controller that performs the route guidance based on the information; a GPS-communication controller that cuts off the communication with the GPS when the information is not acquired; and a server-communication controller that cuts of a communication with the navigation server when the information is not acquired.

TECHNICAL FIELD

The present invention relates to a navigation device, a navigationmethod, and a navigation program.

BACKGROUND ART

A conventional navigation device, such as a car navigation system, has afunction of searching a route from a place of departure to adestination. Generally, such a navigation device also has a function ofrerouting (researching a route afterwards) when a current location thatis determined by a global positioning system (GPS) is deviated by morethan a predetermined distance from a route that was searched andselected at the place of departure. The rerouting is performedautomatically, since an operation of the navigation device by a userwhile driving the vehicle is dangerous.

Some navigation devices perform the automatic rerouting under apredetermined condition. For example, the following patent document 1discloses a technology that does not perform the rerouting when avehicle is near any point on the route to the destination, even if thevehicle has deviated from the route.

Moreover, the following patent document 2 discloses a technology thatdisplays, according to a request from a user, a new route that wasresearched and stored in the navigation device in the background(irrespective of whether the automatic rerouting setting has been doneor not) when the vehicle was deviated from a route to the destination.

Moreover, the following patent document 3 discloses a technology thatdoes not perform the rerouting when a vehicle is near a turnoff on arecommended route, even if the vehicle has deviated from the route.

On the other hand, in recent years, a navigation device not only for acar driver but also for a user who is walking or taking a train or a bushas been proposed (refer to the following patent document 3, forexample).

Patent document 1: Japanese Patent Application Laid-open Publication No.H8-159797

Patent document 2: Japanese Patent Application Laid-open Publication No.H9-152352

Patent document 3: Japanese Patent Application Laid-open Publication No.2000-241182

Patent document 4: Japanese Patent Application Laid-open Publication No.2000-258184

DISCLOSURE OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

Generally, such a navigation device are mounted on a portable telephone,and such a portable navigation device, unlike a car navigation device,has a peculiar problem as explained below.

That is, a user who is walking along the footway may be unable toreceive radio waves (indicating the current location) from the GPSsatellite, because the radio waves tend to be blocked by buildings. As aresult, the current location shown on a screen of the portablenavigation device cannot be accurate (for example, a mark indicating thecurrent location can hop within the screen).

Moreover, the portable navigation device, which does not have anautonomous navigation sensor as mounted on a vehicle, tends to snake. Itis difficult to acquire precise data on traveling of the portablenavigation device, and thereby to display precise current locationthereof.

Further, it is difficult to perform an accurate map matching since theintervals between the footways, which can be narrower than the roadssubjected to route searching for a vehicle, on a map can be very small.

Thus, such a portable navigation device has a lower accuracy indetermining the current location than that of a general car navigationdevice. Therefore, it is not possible to perform route guidanceaccurately even if the communication with the GPS satellite is continuedand power is consumed in the communication. Particularly, in theportable navigation device, unnecessary power consumption is a majorproblem since a battery capacity thereof is small.

Further, the portable navigation device cannot hold map data, which issubjected to a route search and is displayed on a screen, since thestorage area thereof is limited. When performing route guidance ordisplaying a map, the portable navigation device establishes acommunication with a navigation server, which is connected to theportable navigation device via a network and stores the map data, toreceive the map data or a route data.

Therefore, the portable navigation device has to communicate with thenavigation server whenever the current location is not determined or theuser selects a route largely different from the recommended route,thereby increasing communication charges with the navigation server.

The present invention is made in a view of the abovementioned problem,and it is an object of the present invention to provide a navigationdevice, a navigation method, and a navigation program that can reducepower consumption as well as communication charges when the currentlocation cannot be determined.

MEANS TO SOLVE THE PROBLEMS

To solve the problem and achieve the object, a navigation deviceaccording to an aspect of the present invention, which performs a routeguidance based on a route that is selected from among a plurality ofroutes to a destination including a walking route, includes: a locationacquiring unit that acquires information about a current location byperforming a communication with a global positioning system; aguidance-control unit that determines whether the information about thecurrent location is acquired by the location acquiring unit, and whendetermining that the information about the current location is acquired,performs the route guidance based on the information about the currentlocation; and a global-positioning-system-communication controlling unitthat cuts of the communication with the global positioning system whenthe guidance-control unit determines that the information about thecurrent location is not acquired.

A navigation device according to another aspect of the presentinvention, which performs a route guidance based on a route that isselected from among a plurality of routes to a destination including awalking route, includes: a location acquiring unit that acquiresinformation about a current location by performing a communication witha global positioning system; a guidance-information acquiring unit thatacquires information about the route selected from a server that isconnected to a network and stores information about the routes; aguidance-control unit that determines whether the information about thecurrent location is acquired by the location acquiring unit, and whendetermining that the information about the current location is acquired,performs the route guidance based on the information about the currentlocation and the information about the route selected; and aserver-communication controlling unit that cuts off a communication withthe server when the guidance-control unit determines that theinformation about the current location is not acquired.

A navigation method according to still another aspect of the presentinvention, which is for performing a route guidance based on a routethat is selected from among a plurality of routes to a destinationincluding a walking route, includes: acquiring information about acurrent location by performing a communication with a global positioningsystem; determining whether the information about the current locationis acquired at the acquiring; performing the route guidance based on theinformation about the current location when it is determined at thedetermining that the information about the current location is acquired;and cutting of the communication with the global positioning system whenit is determined at the determining that the information about thecurrent location is not acquired.

A navigation method according to still another aspect of the presentinvention, which is for performing a route guidance based on a routethat is selected from among a plurality of routes to a destinationincluding a walking route, includes: acquiring information about acurrent location by performing a communication with a global positioningsystem; acquiring information about the route selected from a serverthat is connected to a network and stores information about the routes;determining whether the information about the current location isacquired at the acquiring; performing the route guidance based on theinformation about the current location and the information about theroute selected when it is determined at the determining that theinformation about the current location is acquired; and cutting off acommunication with the server when it is determined at the determiningthat the information about the current location is not acquired.

A navigation program according to still another aspect of the presentinvention, which is for performing a route guidance based on a routethat is selected from among a plurality of routes to a destinationincluding a walking route, causes a computer to execute: determiningwhether information about a current location is acquired by performing acommunication with a global positioning system; performing the routeguidance based on the information about the current location when it isdetermined that the information about the current location is acquired;and cutting off the communication with the global positioning systemwhen it is determined that the information about the current location isnot acquired.

A navigation program according to still another aspect of the presentinvention, which is for performing a route guidance based on a routethat is selected from among a plurality of routes to a destinationincluding a walking route, causes a computer to execute: acquiringinformation about the route selected from a server that is connected toa network and stores information about the routes; determining whetherinformation about a current location is acquired by performing acommunication with a global positioning system; performing the routeguidance based on the information about the current location when it isdetermined that the information about the current location is acquired;and cutting off a communication with the server when it is determinedthat the information about the current location is not acquired.

EFFECTS DUE TO THE INVENTION

According to the present invention, information about the currentlocation is acquired by performing communication with a globalpositioning system (GPS). Then it is determined whether the informationabout the current location is acquired, and when the information aboutthe current location is acquired, a route guidance is performed based onthe information about the current location. When the information aboutthe current location is not acquired, the communication with the GPS iscut off. As a result, when the route guidance cannot be performed sincethe current location cannot be acquired, the communication with the GPSdoes not performed, thereby reducing power consumption.

Moreover, according to the present invention, the information about thecurrent location is acquired by performing the communication with theGPS, whereas information about a selected route is acquired from aserver that is connected to a network and stores information aboutroutes. Then it is determined whether the information about the currentlocation is acquired, and when the information about the currentlocation is acquired, the route guidance is performed based on theinformation about the current location and the information on theselected route. When the route guidance cannot be performed since theinformation about the current location cannot be acquired, thecommunication with the server is cut off not to receive map informationand route information from the server, thereby reducing communicationcharges.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a navigation system including a navigationdevice according to an embodiment of the present invention.

FIG. 2 is a flowchart of an overall procedure of route guidanceperformed by the navigation system.

FIG. 3 is a flowchart of a route guidance process performed by thenavigation device.

FIG. 4 is a flowchart of a route guidance process performed by aguidance controller.

FIG. 5 is an example of a display screen of a message of termination.

FIG. 6 is an example of a menu screen.

DESCRIPTION OF SIGNS

-   100 navigation device-   110 display unit-   111 voice output unit-   112 voice input unit-   114 GPS unit-   115 communication unit-   116 input unit-   117, 617 controlling unit-   120 guidance controller-   130 display controller-   140 guiding voice controller-   150 GPS-communication controller-   160 navigation-information acquiring unit-   170 server-communication controller-   200 network-   300 navigation server-   310 map delivery unit-   320 map database-   330 route searching unit

BEST MODE FOR CARRYING OUT THE INVENTION

Exemplary embodiments of a navigation device, a navigation method, and anavigation program are described below in detail with reference to theaccompanying drawings. The navigation devices according to theembodiments are a portable telephone in which the navigation programaccording to the present invention installed.

FIG. 1 is a block diagram of a navigation system including a navigationdevice according to a first embodiment. As shown in FIG. 1, thenavigation system includes a navigation device 100, a network 200, and anavigation server 300.

The network 200 is a network such as a portable telephone network andthe Internet. The navigation device 100 and the navigation server 300can exchange various data via the network 200.

The navigation device 100 according to the first embodiment is aportable navigation device that also functions as a portable telephone,and includes a display unit 110, a voice output unit 111, a voice inputunit 112, GPS unit 114, a communication unit 115, an input unit 116, anda controlling unit 117.

The display unit 110 has a Liquid Crystal Display (LCD) and displaysvarious information (such as map data) supplied from the controllingunit 117. The voice output unit 111 has a speaker and outputs voice datasupplied from the controlling unit 117. The voice input unit 112 has amicrophone, creates voice data corresponding to a voice input by a user,and outputs the voice data to the controlling unit 117. The voice inputunit 112 is used for inputting voice of the user when the navigationdevice 100 functioning as a telephone.

The GPS unit 114 has a GPS antenna etc. and outputs information aboutthe current location, which includes coordinates of the current locationthat are determined based on information received from a satellite, to aguidance controller 120 of the controlling unit 117. When the GPS unit114 could not have acquired the information about the current locationdue to defective communication, it outputs error information to theguidance controller 120. The GPS unit 114 performs communication andcutting-off the communication with a GPS satellite by radio waves underthe control of a GPS communication controller 150.

The communication unit 115 has a structure similar to that of a generalportable telephone. The communication unit 115 includes an antenna andtransfers various data (such as voice data and map data) to and fromother communication terminal (such as a portable telephone and a Webserver) via the network 200 under a control of the controlling unit 117.The input unit 116 has a numerical pad, creates a signal according to anoperation by the user, and outputs the signal to the controlling unit117. A server-communication controller 170 of the controlling unit 117controls the communication unit 115 to establish or cut offcommunication with the navigation server 300 via the network 200.

The controlling unit 117 has a Central Processing Unit (CPU) and astorage unit such as a Read Only Memory (ROM) and a Random Access Memory(RAM). The controlling unit 117 controls the entire navigation device100 (in other words, each unit of the device) so that the navigationdevice 100 functions as the portable telephone, by executing anavigation program that is stored in the storage unit.

Moreover, the controlling unit 117 of the navigation device 100according to the first embodiment controls each unit to executenavigation functions such as a map display and a route guidance. Moreconcretely, the controlling unit 117 includes a guidance controller 120,a display controller 130, a guiding voice controller 140, aGPS-communication controller 150, a navigation-information acquiringunit 160, and the server-communication controller 170. Here, thenavigation-information acquiring unit 160 forms a guidance-informationacquiring unit according to the present invention.

The display controller 130 creates display data based on map datadelivered from the navigation server 300, and controls the display unit110 to display the map data. Moreover, the display controller 130creates display data of various information necessary for navigation,such as characters and patterns. The display unit 110 displays thedisplay data created by the display controller 130, thereby displaying amap indicating a route to be guided, or characters such as “turn to theright”.

The guiding voice controller 140 outputs voice data, which correspondsto a voice to be output from the voice output unit 111, to the voiceoutput unit 111 at a predetermined timing during route guidance. Forexample, when a user of the navigation device 100 comes to a point 30mbefore an intersection where it is supposed to take a right turn, theguiding voice controller 140 outputs the voice data of a voice such as“right turn at next intersection”.

Thus, according to the first embodiment, the display unit 110, the voiceoutput unit 111, the display controller 130, the guiding voicecontroller 140 perform route guidance for guiding the user along theroute, under the control of the guidance controller 120.

The guidance controller 120 controls the above units as mentioned aboveto perform route guidance. More concretely, the guidance controller 120controls each unit based on the current location notified by the GPSunit 114 and a route selected by the navigation server 300, and causesthe units to display guidance information or to provide voice guidance.

Moreover, the guidance controller 120 determines whether the GPS unit114 has acquired the information about the current location by an inputfrom the GPS unit 114. In other words, if the input from the GPS unit114 includes the coordinates of the location, the guidance controller120 determines that the GPS unit 114 has acquired the information aboutthe current location, and performs the route guidance. On the otherhand, if the input from the GPS unit 114 includes error information, theguidance controller 120 determines that the GPS unit 114 has notacquired the information about the current location. In this case, theguidance controller 120 calculates the number of errors, and if thenumber of errors has reached 4 or more than 4, outputs to theGPS-communication controller 150 a request to cut off the communicationwith the GPS, and outputs to the server-communication controller 170 arequest to cut off the communication with the navigation server 300.

An upper limit of the number of errors is not restricted to 4 and can beset voluntarily.

Furthermore, the guidance controller 120 determines whether thecoordinates of the current location input from the GPS unit 114 aredeviated by more than a predetermined distance (for example, more than100 m) from the route selected by the user from among a plurality ofroutes to the destination, by comparing the coordinates of the route andcoordinates of the current location.

The current location can be deviated from the route by more than thepredetermined distance not only when the user has deviated from theroute intentionally, but also when the current location is wronglyidentified since precise coordinates of the current location cannot beacquired from the GPS, and when the current location is displayedwrongly on a map in a map matching process.

When determining that the information about the current location inputfrom the GPS unit 114 is deviated by more than the predetermineddistance from the route selected by the user, the guidance controller120 calculates the number of errors. When the number of errors reaches 4or more than 4, the guidance controller 120 outputs a request to theGPS-communication controller 150 to cut off the communication with theGPS, and outputs a request to the server-communication unit 170 to cutoff the communication with the navigation server 300.

An upper limit of the number of errors is not restricted to 4 and can beset voluntarily. Moreover, the distance between the route and thecurrent location is not restricted to 100 m and can be set voluntarily.

The navigation-information acquiring unit 160 makes an access to thenavigation server 300 via the communication unit 115 and the network200, and makes a request for sending information necessary fornavigation such as map data for displaying a map on the display unit110, and data indicating a result of route search from a place ofdeparture to a destination.

More concretely, the navigation-information acquiring unit 160, whichacquires information on the current location periodically from the GPSunit 114, sends a request for map data including the current location tothe navigation server 300 if the navigation-information acquiring unit160 has not yet received the map. The navigation-information acquiringunit 160 also sends to the navigation server 300 a request for routesearch that includes information necessary for route search, such as theplace of departure (it can be the current location or can be set by theuser), the destination, a point of passing, and other search conditionssuch as search priority (shorter time/low cost). Then, thenavigation-information acquiring unit 160 acquires the result of theroute search and the map data that is sent from the navigation server300 responding to the request, and supplies it to the display controller130.

The GPS-communication controller 150 starts communication with the GPSwhen the user instructs to start the route guidance through an initialmenu (not shown). On the other hand, the GPS-communication controller150 cuts off the communication with the GPS when a request to cut offthe communication is input from the guidance controller 120. As aresult, the GPS unit 114 does not receive radio waves from the GPSsatellite any more.

The server-communication controller 170 establishes communication withthe navigation server 300 when the start of the route guidance isselected in an initial menu (not shown in the diagram). On the otherhand, the server-communication controller 170 cuts off the communicationwith the navigation server 300 when the guidance controller 120requests, to stop receiving any data from the navigation server 300.

Next, the navigation server 300 is described. The navigation server 300,as shown in FIG. 1, includes a map delivery unit 310, a map database(DB) 320, and a route searching unit 330.

The map database 320 is a database that stores the map data. The mapdelivery unit 310, when receiving a request from the navigation device100 (or other navigation device) including the current location thereof,acquires map data including the current location and sends the map datato the navigation device 100 via the network 200.

The route searching unit 330, when receiving a request for route searchfrom the navigation device 100, searches a plurality of routes up to thedestination from the place of departure (the destination and the placeof departure are included in the request), and sends the result of theroute search to the navigation device 100 via the network 200. The routesearching unit 330 of the navigation server 300 according to the firstembodiment can search not only a car route but also other routes such asa walking route, a bus route, a train route, and a combination thereof.The car route means a route for a vehicle that the user can driveanywhere he/she wants, such as a vehicle for private use and amotorcycle, and does not include a bus route etc. that is determined inadvance.

Next, a process of route guidance performed by the navigation system,which includes the navigation device 100 and the navigation server 300according to the first embodiment, is described. FIG. 2 is a flowchartof overall process of route guidance performed by the navigation systemaccording to the first embodiment.

The user of the navigation device 100 according to the first embodimentinputs in the navigation device 100, through the input unit 116, searchconditions such as a place of departure and a destination, and makes arequest for route search. The navigation device 100 sends the requestfor route search, which includes the search conditions, to thenavigation server 300 via the network 200 (step S201).

The navigation server 300, which has received the request for routesearch from the navigation device 100, performs route search accordingto the search conditions included in the request for route search (stepS202). Then the navigation server 300 sends the result of route searchto the navigation device 100 via the network 200 (step S203).

The navigation device 100, which has received the result of routesearch, displays a search result screen on the display unit 110 (stepS204).

In the search result screen, the user can input instructions such as“start route guidance” or “check route map” through the input unit 116of the navigation device 100.

Next, a route guidance process that is performed by the navigationdevice 100 according to the first embodiment is described. FIG. 3 is aflowchart of the route guidance process performed by the navigationdevice 100.

When the user instructs the navigation device 100 to start the routeguidance through the initial menu (not shown), a start message isdisplayed on the display unit 110 under the control of the displaycontroller 130 (step S301). Then, the guidance controller 120 acquiresthe information about the current location from the GPS unit 114, whichreceives the information from the GPS satellite and outputs it to theguidance controller 120 (step S302).

Next, the guidance controller 120 determines whether the acquisition ofthe information about the current location has failed, by checking theinformation includes error information or coordinates of the currentlocation (step S303). When the information from the GPS unit 114includes error information, the guidance controller 120 determines thatthe acquisition of the information about the current location has failed(Yes at step S303), and increments the number of errors (step S304).

Next, till the number of errors reaches 4 (No at step S305), theguidance controller 120 repeats the acquisition of the information aboutthe current location, the determination of whether the acquisition hasfailed or not, and incrementing the number of errors. Then, when thenumber of errors reaches 4 (Yes at step S305), in other words, when theacquisition of the information about the current location from the GPSsatellite fails continuously for four times, the guidance controller 120outputs the request to the GPS-communication controller 150 to cut offthe communication. The GPS-communication controller 150, which hasreceived the request, cuts off the communication with the GPS (stepS306). Afterwards, the navigation device 100 does not receive radiowaves from the GPS satellite.

Next, the guidance controller 120 outputs the request to cut off thecommunication to the server-communication controller 170.

The server-communication controller 170, which receives the request,cuts off the communication with the navigation server 300 in the network200 (step S307). Afterwards, the navigation device 100 does not receivethe map data and route data from the navigation server 300.

Then, a message of termination is output to the display unit 110 by thedisplay controller 130 (step S308), and the route guidance process isterminated.

FIG. 5 is an example of a display screen of the message of termination.As shown in FIG. 5, on the termination message display screen, a messageto the effect that the current location could not be checked isdisplayed.

Therefore, when a condition of being unable to acquire the informationabout the current location continues successively, the communicationwith the GPS is cut off and the map data and the route data are notreceived from the navigation server 300. As a result, the route guidanceprocess is not performed.

At step S303, if the information about the current location thatincludes the location coordinates could have been acquired by theguidance controller 120 from the GPS unit 114 (No at step S303), theguidance controller 120 compares the location coordinates of theinformation about the current location acquired and location coordinatesof the route that the user selected, and determines whether the currentlocation is deviated from the route by more than the predetermineddistance or not (for example 100 m) (step S309). Then, if it isdetermined to be deviated by more than the predetermined distance, (Yesat step S309), the guidance controller 120 determines it to be an error,and increases the number of errors just by 1 (step S310).

Any voluntary distance can be determined as the predetermined distance.In a case of a portable navigation, the current location is indicatedwrongly and tends to be map matched with an adjacent road and thecurrent location tends to fluctuate. On the other hand, a travelingvelocity is slow during walking, and when the user realizes havingmistaken the route, it is possible to return to a correct route fromthat location. Moreover, the user can take enough time to have a look atthe screen and determines whether the route has been mistaken or not.Therefore, it is not necessary to perform an automatic researching ofthe route immediately. If the route and the current location that isdeviated from the route are displayed on the display unit 110 of thenavigation device, the user can return to the correct route. Moreover,since the user, unlike a driver of a vehicle, can check a situationaround, in a case where the current location is temporarily displayedwrongly without doubt, since it is possible to continue walking whilenoticing the display, it is not necessary to perform the automaticresearching of the route immediately. Therefore, about 100 m is adesirable distance for determining whether deviated from the route ornot.

Next, till the number of errors becomes 4 or more than 4 (step S311),the guidance controller 120 acquires repeatedly the information aboutthe current location, determines whether the acquisition of theinformation about the current location has failed or not, determineswhether the current location is deviated from the route by thepredetermined distance, and increases the number of errors (No at stepS311). Then, when the number of errors reaches 4 or more than 4 (Yes atstep S311), in other words, if the current location is determinedsuccessively for four time to have been deviated by more than thepredetermined distance, it outputs the request to the GPS-communicationcontroller 150 to cut off the communication, and the GPS-communicationcontroller 150 that receives this request cuts off the communicationwith the GPS (step S312). Afterwards, the navigation device 100 does notreceive the satellite radio waves.

The determination of the current location being deviated from the routeby more than the predetermined distance is made and the communicationwith the navigation server 300 and the GPS communication is cut off fortrying to acquire once again the correct information about the currentlocation for the reason that the user has not deviated from the routeintentionally, but because for not being able to acquire the correctinformation about the current location, and when the current location isidentified wrongly and is displayed upon deviating from the correctcurrent location on the display unit 110.

Next, the guidance controller outputs to the server-communicationcontroller 170 the request to cut off the communication, and theserver-communication controller 170 that receives the request cuts ofthe communication with the navigation server 300 in the network 200(step S313). Afterwards, the navigation device 100 does not receive themap data and the route data from the navigation server 300.

Further, the display controller 130 displays a menu on the display unit110 (step S314). FIG. 6 is an example of the menu screen. Since thecurrent location is deviated from the route (route), a message ofwhether a rerouting (researching of the route) is to be performed or notis displayed on the menu screen as shown in FIG. 6.

Next, the guidance controller 120 determines whether the researching ofthe route is designated by an input by the user from the menu screen(step S315). If the user selects “Yes” on the menu screen, it means thatthe researching of the route is designated (Yes at step S315), and theguidance controller 120 performs a researching process of the route upto a destination from the current location that is deviated from theroute (step S316), and then the process returns to step S301.

On the other hand, if the user selects “No” on the menu screen, it meansthat the researching of the route is not designated (No at step S315),and the researching of the route is not performed, and the process isterminated.

At step S309, when the guidance controller 120 does not determine thatthe current location is deviated from the route by more than thepredetermined distance (No at step S309), the route guidance process bythe guidance controller 120 is performed (step S317).

FIG. 4 is a flowchart that indicates a procedure of the route guidanceprocess at step S317.

To start with, the display controller 130 displays by superimposing thecurrent location on the map that is displayed on the display unit 110(step S401). Next, the route guidance is performed by the guidancecontroller 120 (step S402), and the number of errors when theacquisition of the current location has failed and the number of errorswhen the current location is deviated from the route by more than thepredetermined distance, are initialized (step S403). Then, the guidancecontroller 120 determines whether the user has reached the destination(step S404). If it is determined that the user has reached thedestination (Yes at step S404), the message of termination (not shown inthe diagram) is displayed on the display unit 110 by the displaycontroller 130 (step S405).

If it is determined that the user does not have reached the destination(No at step S404), the process returns to step S301 in FIG. 3, and aprocess of acquiring the information about the current location isrepeated.

Thus, in the navigation device 100 according to the embodiment, sincethe GPS unit 114 acquires the information about the current location bythe communication with the GPS, the guidance controller 120 determineswhether the information about the current location is acquired or not,if it is determined not to have acquired the information about thecurrent location, the GPS-communication controller 150 cuts off thecommunication with the GPS, and the server-communication controller 170cuts off the communication with the navigation server 300, if thecurrent location cannot be acquired and if the route guidance becomesimpossible, it is possible to reduce the unnecessary power consumption,moreover, it becomes unnecessary to receive the map data from thenavigation server 300, and it is possible to reduce the load of thecommunication charges.

Moreover, in the navigation device 100 according to the embodiment, ifthe current location is identified wrongly, or if the user intentionallyis deviated from the route up to the destination and the currentlocation is away from the route by more than the predetermined distance,since the GPS-communication controller 150 cuts off the communicationwith the GPS and the server-communication controller 170 cuts of thecommunication with the navigation server 300, it is possible to reducethe unnecessary power consumption, moreover it becomes unnecessary toreceive the map data from the navigation server 300, and it is possibleto reduce the load of the communication charges.

Moreover, the navigation device 100 according to the embodiment cuts offthe communication with the GPS and the navigation device 100 when theacquisition of the information about the current location has failed orthe current location has been deviated for four times. However, thecommunication with the GPS and the communication with the navigationserver 300 can be cut off immediately, without counting the number oferrors, after the acquisition of the information about the currentlocation has failed or the current location has been deviated.Particularly, when the communication with the GPS and the communicationwith the navigation device 100 are cut off immediately after the currentlocation has been deviated, the communication with the GPS and thecommunication with the navigation device 100 are cut off immediately, itbecomes possible to improve an efficiency of the process when the userhas deviated intentionally from the route.

Moreover, according to the embodiment, the CPU of a controlling unit hasbeen let to perform a process including a guidance process as mentionedabove according to a computer program that is stored in a storage unitof the ROM, however an arrangement may be made to provide a computerprogram for causing a computer to perform a similar process, to the userby a communication line such as the internet, or an arrangement may bemade to record the computer program on a computer readable recordingmedium such as a CD-ROM (Compact Disc-Read only Memory) and to provideto the user. Moreover, the navigation device may be structured torealize by a dedicated hardware line that performs the process mentionedabove, and be provided to the user.

INDUSTRIAL APPLICABILITY

Thus, a navigation device, a navigation method, and a navigation programaccording to the present invention are useful in route guidance using aportable navigation device.

1-12. (canceled)
 13. A navigation device that performs a route guidancebased on a route that is selected from among a plurality of routes to adestination including a walking route, the navigation device comprising:a location acquiring unit that acquires information about a currentlocation by performing a communication with a global positioning system;a guidance-control unit that determines whether the information aboutthe current location is acquired by the location acquiring unit, andwhen determining that the information about the current location isacquired, performs the route guidance based on the information about thecurrent location; and a global-positioning-system-communicationcontrolling unit that cuts off the communication with the globalpositioning system when the guidance-control unit determines that theinformation about the current location is not acquired.
 14. Thenavigation device according to claim 13, wherein theglobal-positioning-system-communication controlling unit cuts off thecommunication with the global positioning system when theguidance-control unit has determined that the information about thecurrent location is not acquired for a predetermined number of times.15. The navigation device according to claim 13, wherein theguidance-control unit determines whether the current location isdeviated from the route selected, by a predetermined distance, based onthe information about the current location acquired by thelocation-information acquiring unit and information about a location ofthe route selected, and the global-positioning-system-communicationcontrolling unit cuts off the communication with the global positioningsystem when the guidance-control unit determines that the currentlocation is deviated from the route selected by the predetermineddistance.
 16. The navigation device according to claim 15, wherein theglobal-positioning-system-communication controlling unit cuts off thecommunication with the global positioning system when theguidance-control unit has determined that the information about thecurrent location is not acquired for a predetermined number of times.17. A navigation device that performs a route guidance based on a routethat is selected from among a plurality of routes to a destinationincluding a walking route, the navigation device comprising: a locationacquiring unit that acquires information about a current location byperforming a communication with a global positioning system; aguidance-information acquiring unit that acquires information about theroute selected from a server that is connected to a network and storesinformation about the routes; a guidance-control unit that determineswhether the information about the current location is acquired by thelocation acquiring unit, and when determining that the information aboutthe current location is acquired, performs the route guidance based onthe information about the current location and the information about theroute selected; and a server-communication controlling unit that cutsoff a communication with the server when the guidance-control unitdetermines that the information about the current location is notacquired.
 18. The navigation device according to claim 17, wherein theserver-communication controlling unit cuts off the communication withthe server when the guidance-control unit has determined that theinformation about the current location is not acquired for apredetermined number of times.
 19. The navigation device according toclaim 17, wherein the guidance-control unit determines whether thecurrent location is deviated from the route selected, by a predetermineddistance, based on the information about the current location acquiredby the location-information acquiring unit and information about alocation of the route selected, and the server-communication controllingunit cuts off the communication with the server when theguidance-control unit determines that the current location is deviatedfrom the route selected by the predetermined distance.
 20. Thenavigation device according to claim 19, wherein theserver-communication controlling unit cuts off the communication withthe server when the guidance-control unit has determined that theinformation about the current location is not acquired for apredetermined number of times.
 21. A navigation method for performing aroute guidance based on a route that is selected from among a pluralityof routes to a destination including a walking route, the navigationmethod comprising: acquiring information about a current location byperforming a communication with a global positioning system; determiningwhether the information about the current location is acquired at theacquiring; performing the route guidance based on the information aboutthe current location when it is determined at the determining that theinformation about the current location is acquired; and cutting off thecommunication with the global positioning system when it is determinedat the determining that the information about the current location isnot acquired.
 22. A navigation method for performing a route guidancebased on a route that is selected from among a plurality of routes to adestination including a walking route, the navigation method comprising:acquiring information about a current location by performing acommunication with a global positioning system; acquiring informationabout the route selected from a server that is connected to a networkand stores information about the routes; determining whether theinformation about the current location is acquired at the acquiring;performing the route guidance based on the information about the currentlocation and the information about the route selected when it isdetermined at the determining that the information about the currentlocation is acquired; and cutting off a communication with the serverwhen it is determined at the determining that the information about thecurrent location is not acquired.
 23. A navigation program forperforming a route guidance based on a route that is selected from amonga plurality of routes to a destination including a walking route, thenavigation program causes a computer to execute: determining whetherinformation about a current location is acquired by performing acommunication with a global positioning system; performing the routeguidance based on the information about the current location when it isdetermined that the information about the current location is acquired;and cutting off the communication with the global positioning systemwhen it is determined that the information about the current location isnot acquired.
 24. A navigation program for performing a route guidancebased on a route that is selected from among a plurality of routes to adestination including a walking route, the navigation program causes acomputer to execute: acquiring information about the route selected froma server that is connected to a network and stores information about theroutes; determining whether information about a current location isacquired by performing a communication with a global positioning system;performing the route guidance based on the information about the currentlocation when it is determined that the information about the currentlocation is acquired; and cutting off a communication with the serverwhen it is determined that the information about the current location isnot acquired.